Which process of wastewater treatment occurs in septic tanks?

In septic tanks, the primary process at work is biological decomposition. This occurs as waste enters the tank and is broken down by bacteria and other microorganisms that naturally occur in the system. These microorganisms digest organic materials, converting them into simpler compounds, which is a critical component of wastewater treatment.

The design of a septic tank promotes anaerobic conditions (absence of oxygen), enabling these bacteria to thrive and effectively decompose waste. Over time, the process reduces the volume of solids within the tank, allowing clearer liquid effluent to be released into the drain field, where further treatment can occur as the effluent percolates through the soil.

In contrast to biological decomposition, other options such as mechanical filtration and physical separation may apply to different treatment systems but are not primarily associated with the function of a septic tank. Mechanical filtration typically involves physical barriers to remove particles from the water, and physical separation can refer to processes that do not rely on biological activity. Therefore, biological decomposition is the key process that defines how septic tanks manage and treat wastewater.